Non-volatile memory

ABSTRACT

A nonvolatile memory includes at least a first electrode ( 71 ) and a second electrode ( 72 ) provided on a substrate, the first and second electrodes being separated from each other, and a conductive organic thin film ( 73 ) for electrically connecting the first and second electrodes. The conductive organic thin film ( 73 ) has a first electric state in which it exhibits a first resistance, and a second electric state in which it exhibits a second resistance. A first threshold voltage for a transition from the first electric state to the second electric state, and a second threshold voltage for a transition from the second electric state to the first electric state are different from each other, and either the first electric state or the second electric state is maintained a voltage in a range between the first threshold voltage and the second threshold voltage.

TECHNICAL FIELD

The present invention relates to a nonvolatile memory including aconductive organic thin film. More specifically, it relates to anonvolatile memory, as an application example of a memory, suitable foruse in a memory card or a computer system, as an auxiliary storagemedium that maintains information even after the power is turned off,and hence, does not need backup with the use of batteries.

BACKGROUND ART

Recently, the increasing demand for computers, particularly personalcomputers (hereinafter abbreviated as “PC”), in response to an explosiveexpansion of the Internet has caused the industries in the field todevelop rapidly. The market has demanded products of higher performanceand lower costs, which leads to a fierce competition on the supply sidethat has been trying to meet the demand. One of the significant factorsin determining the performance of a computer is a storage device, andthe mainstream of the same is a semiconductor memory configured so thatmemory cells are formed on a semiconductor substrate such as silicon.The main requirements for the high performance of the semiconductormemory are “high speed of input/output to/from memory”, “large capacityof memory”, and “stability of storage”. Computers may have variousconfigurations to meet various demands of the market, but in the casewhere both of the higher speed and the larger capacity are pursued, thecost rises, whereas in the case where a compromise is made by giving upeither of the two, the cost can be reduced.

Currently, the most common memories built in PCs are configured so thatcache memories and main memories are composed of RAMs (random accessmemories), and examples of memories used as such include DRAMs (dynamicrandom access memories) and SRAMs (static random access memories).

A DRAM has a larger capacity per unit area as compared with a SRAM andis manufactured at a lower cost, whereas it has a problem that an outputof memory takes time since the retrieval of memory is carried out bydischarging electric charges, and moreover, the supply of charges(refresh) is required at all times.

On the other hand, in the case of a SRAM, since the retrieval of memorytherefrom is carried out by determining a state of a multivibrator,refreshing is not required, and the reading is performed at a highspeed. However, because of a complex structure thereof, the SRAM has asmaller capacity per unit area, and is expensive, as compared with aDRAM.

Therefore, a common memory configuration in a PC is such that a SRAM isused as a cache memory and a DRAM is used as a main memory so that thecost is suppressed. Further, since the memory in the DRAM and SRAMdisappears when the power is turned off, necessary memory has to bestored in another storage device such as a disk. Examples of storagedevices in which memory is not lost even after the power is turned offinclude a flash memory, but considering its need for high voltage uponinput, its limited capacity, and its cost, it hardly satisfies theabove-described demands of the market at the present time.

For the downsizing and speed enhancement of a computer, a storage devicein the computer has to have a large capacity. As to a DRAM as a typicalinternal memory, the dense packaging has been attempted by reducing thecell size, but insufficient capacity of a capacitor has been a problem.More specifically, though various cell structures have been studied forincreasing an electrode area, they are significantly complex structures,and there arise problems such as an increase in the cost per one bit andan increased ratio of defects that occur during manufacturing.

As a conventional example, a scheme for recording/reproducinginformation in/from a medium by detecting current flowing through anelement with use of a probe electrode has been proposed, the mediumbeing obtained by laminating a recording film having an electric memoryeffect on an amorphous carbon layer formed on a substrate electrode (JP5(1993)-28549A).

However, in the foregoing scheme, the organic film is not chemicallybonded with a surface of a substrate and is separated therefrom easily.Additionally, it needs further improvement regarding electriccharacteristics.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a nonvolatile memorythat not only allows writing/reading of record to be performed utilizinga change in an electrical resistance of a conductive organic thin film,but also can be densely packaged.

To achieve the foregoing object, a nonvolatile memory of the presentinvention includes:

at least a first electrode and a second electrode provided on asubstrate, the first and second electrodes being separated from eachother; and

a conductive organic thin film for electrically connecting the first andsecond electrodes,

wherein

the conductive organic thin film has a first electric state in which itexhibits a first resistance, and a second electric state in which itexhibits a second resistance,

a first threshold voltage for a transition from the first electric stateto the second electric state, and a second threshold voltage for atransition from the second electric state to the first electric stateare different from each other,

either the first electric state or the second electric state ismaintained at a voltage in a range between the first threshold voltageand the second threshold voltage,

the conductive organic thin film is formed with organic molecules, eachof which includes:

-   -   a terminal binding group that is bound with a surface of the        substrate or a surface of an insulation layer on the substrate        by a covalent bond; and    -   a conjugate group,        and,

each conjugate group is polymerized with another conjugate group ofanother organic molecule so as to form the conductive organic thin film.

Further, another nonvolatile memory of the present invention isconfigured so that the first electrode is a source electrode and thesecond electrode is a drain electrode,

the nonvolatile memory further comprising a gate electrode, a contactelectrode, and a horizontal selection line,

wherein

the contact electrode is connected with the horizontal selection line,

the source electrode and the drain electrode are arranged to extend in adirection crossing the horizontal selection line orthogonally,

the gate electrode is arranged at a position above or below a regionbetween the source electrode and the drain electrode, the position beingapart from the source electrode and the drain electrode,

the conductive organic thin films are arranged so as to electricallyconnect the contact electrode, the source electrode, and the drainelectrode, and

the conductive organic thin film arranged between the contact electrodeand the source electrode forms a memory part.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing an electric behavior of a conductive organicthin film in an example of the present invention.

FIG. 2 is a NMR analysis chart of a pyrrole compound in the example ofthe present invention.

FIG. 3 is an IR analysis chart of the pyrrole compound in the example ofthe present invention.

FIG. 4 is a cross-sectional view of a conductive thin film in an exampleof the present invention.

FIGS. 5A to 5C are views obtained by measurement of conductive organicthin films by AFM in examples of the present invention.

FIGS. 6A to 6F are cross-sectional views illustrating a manufactureprocess in Example 2 of the present invention.

FIG. 7 is a perspective view illustrating a nonvolatile memory in anexample of the present invention.

FIG. 8 is a plan view of a semiconductor disk substrate in anapplication example of the present invention.

FIG. 9 is a conceptual view of a computer system in the applicationexample of the present invention.

FIGS. 10A to 10F are cross-sectional views illustrating a manufacturingprocess in Example 3 of the present invention.

FIGS. 11A to 11D are cross-sectional views illustrating a manufactureprocess in Example 3 of the present invention.

FIG. 12A is a cross-sectional view illustrating a nonvolatile memoryelement in Example 4 of the present invention, and FIG. 12B is apartially enlarged perspective view of the same.

FIG. 13 is a view illustrating a chemical reaction state of achemisorption molecule film in Example 4 of the present invention.

FIG. 14 is a view illustrating alignment of chemisorption molecule filmof Example 4 of the present invention.

FIG. 15 is a view illustrating a conductive organic thin film formedafter electrolytic polymerization in Example 4.

FIG. 16 is a partially expanded view of a nonvolatile memory part inExample 4 of the present invention.

FIG. 17 is a wiring diagram for the nonvolatile memory part in Example 4of the present invention.

FIG. 18 is a motion diagram illustrating the nonvolatile memory ofExample 4 of the present invention.

FIG. 19 is a cross-sectional view illustrating a nonvolatile memoryelement of Example 5 of the present invention.

FIG. 20 is a cross-sectional view illustrating another nonvolatilememory element of Example 5 of the present invention.

FIG. 21 is a cross-sectional view illustrating still another nonvolatilememory element of Example 5 of the present invention.

FIG. 22 is a cross-sectional view illustrating still another nonvolatilememory element of Example 5 of the present invention.

FIG. 23 is a cross-sectional view illustrating still another nonvolatilememory element of Example 5 of the present invention.

FIG. 24 is a cross-sectional view illustrating still another nonvolatilememory element of Example 5 of the present invention.

FIG. 25 is a cross-sectional view illustrating still another nonvolatilememory element of Example 5 of the present invention.

FIG. 26 is a cross-sectional view illustrating still another nonvolatilememory element of Example 5 of the present invention.

FIG. 27 is a cross-sectional view illustrating still another nonvolatilememory element of Example 5 of the present invention.

FIGS. 28A to 28C are perspective views illustrating a method foraligning molecules in an example of the present invention.

FIG. 29 is a perspective view illustrating a method for measuringmolecular alignment in an example of the present invention.

DESCRIPTION OF THE INVENTION

In the present invention, a memory cell is used that employs an organicfilm having at least a first conductivity and a second conductivity, towhich at least a first electrode and a second electrode are connected asto be used as input/output terminals, so that the recording,reproduction, and erasure of information is performed using thedifference in the conductivity of the organic film. By so doing, thepresent invention provides a memory with a simpler elementconfiguration.

In the present invention, the conductivity of an organic thin film isattributed to molecules composing an organic molecule aggregate beingpolymerized with one another by conjugated bonds. In the film, aconductive organic thin film (hereinafter also referred to as a“conductive network”) is formed by a polymer that is an aggregate oforganic molecules bound with one another by conjugate bonds that areresponsible for electrical conductivity, thereby having conjugated bondchains (conjugated system). Further, the conductive network is formed soas to extend between electrodes. The conjugated bond chain polymer doesnot range strictly in one direction, but preferably polymer chainsextending in various directions are formed.

In the present invention, a conductivity (ρ) of the conductive organicthin film is not less than 1 S/cm, preferably not less than 1×10³ S/cm,more preferably not less than 5.5×10⁵ S/cm, most preferably not lessthan 1×10⁷ S/cm. These are values under the following conditions: roomtemperature (25° C.); relative humidity of 60%; and no dopant.

The conjugate group that functions in the polymerization preferably isat least one selected from conjugate groups that function in formingpolypyrrole, polythienylene, polyacetylene, polydiacetylene, andpolyacene. In the case where a thin film has conjugate groups thatfunction in forming polypyrrole or polythienylene and is formed byelectrolytic oxidation polymerization, the thin film has a highconductivity.

The terminal binding group preferably forms at least one type of bondselected from a siloxane-type (—SiO—) bond and a SiN— type bond.

The terminal binding group is formed by at least one eliminationreaction selected from the dehydrochlorination, the dealcoholization,and deisocyanation. For instance, in the case where a functional groupat a terminal of a molecule is —SiCl₃, —Si(OR)₃ (where R is an alkylgroup having one to three carbon atoms), or —Si(NCO)₃, while an activehydrogen included in a —OH group, a —CHO group, a —COOH group, a —NH₂group, a >NH group, etc. is present on a surface of the substrate or asurface of a primer coating formed on the substrate, one ofdehydrochlorination, dealcoholization, and deisocyanation occurs,whereby chemisorption molecules are bound by covalent bonds with thesurface of the substrate or the surface of the primer coating formed onthe substrate.

The molecular film formed by this method usually is called“chemisorption film” or “self-assembling film” in the art, but herein itis referred to as “chemisorption film”, and a method for forming thesame is referred to as “chemisorption method”.

In the present invention, the alignment of the molecules preferably isachieved by at least one type of process selected from: an alignmentprocess by rubbing; a tilt draining process of lifting up a substratewith a tilt out of a reaction solution after molecules are bound with asurface of the substrate by covalent bonds through an eliminationreaction; a polarized-light projecting process; and an alignment processutilizing fluctuations of molecules in a polymerization process.

The conductive organic thin film preferably is transparent with respectto light having a wavelength in a visible range. This is because it hasa thickness in the nanometer order (normally not more than 10 nm, evenafter molecular modification, not more than 50 nm), which is muchsmaller than a wavelength in a visible light wavelength range (300 nm to800 nm).

A molecular unit composing the conductive organic thin film preferablyis expressed by, for instance, a formula (1) shown below:

where

B represents hydrogen, an organic group including an alkyl group havingone to ten carbon atoms, an active hydrogen introducible group, or itsresidue,

A represents at least one conjugate bond selected from a pyrrole group,a thienylene group, an acetylene group (an ethynyl group), and adiacetylene group (a diethynyl group),

Z represents at least one functional group selected from an ester group(—COO—), an oxycarbonyl group (—OCO—), a carbonyl group (—CO—), acarbonate group (—OCOO—), and an azo group (—N═N—), or a chemical bond(—),

m and n represent integers satisfying 2≦m+n≦25,

Y represents oxygen (O) or nitrogen (N),

E represents hydrogen or an alkyl group having one to three carbonatoms, and

p represents an integer of 1, 2, or 3.

More specifically, molecule units expressed by chemical formulae (2) to(5) shown below are preferable:

where

X represents hydrogen or an organic group containing an unsaturatedgroup,

q represents an integer of 0 to 10,

Z represents an ester group (—COO—), an oxycarbonyl group (—OCO—), acarbonyl group (—CO—), a carbonate group (—OCOO—), and an azo group(—N═N—), or a chemical bond (—),

E represents hydrogen or an alkyl group having one to three carbonatoms,

m and n represent integers satisfying 2≦m+n≦25, preferably 10≦m+n≦20,and

p represents an integer of 1, 2, or 3.

A chemical compound used for forming the conductive organic thin filmpreferably is expressed by a chemical formula (6) shown below:B—A—(CH₂)_(m)—Z—(CH₂)_(n)—SiD_(p)E_(3−p)  (6)where

B represents hydrogen, an organic group including an alkyl group havingone to ten carbon atoms, or an active hydrogen introducible group,

A represents at least one conjugate bond selected from a pyrrole group,a thienylene group, an acetylene group, and a diacetylene group,

Z represents at least one functional group selected from an ester group(—COO—), an oxycarbonyl group (—OCO—), a carbonyl group (—CO—), acarbonate group (—OCOO—), and an azo group (—N═N—), or a chemical bond(—),

m and n represent integers satisfying 2≦m+n≦25,

D represents at least one reactive group selected from a halogen atom,an isocyanate group, and an alkoxyl group having one to three carbonatoms,

E represents hydrogen or an alkyl group having one to three carbonatoms, and

p represents an integer of 1, 2, or 3.

Further specifically, preferable examples of the chemical compoundinclude: a pyrrolyl compound expressed by a chemical formula (7) shownbelow, a thienyl compound expressed by a chemical formula (8) shownbelow, an ethynyl compound expressed by a chemical formula (9) shownbelow (also referred to as a chemical compound containing an acetylenegroup), and a diethynyl compound expressed by a chemical formula (10)shown below (also referred to as a chemical compound containing adiacetylene group):

X—(CH₂)_(q)—C≡C—(CH₂)_(m)—Z—(CH₂)_(n)—SiD_(p)E_(3−p)  (9)X—(CH₂)_(q)—C≡C—C≡C—(CH₂)_(m)—Z—(CH₂)_(n)—SiD_(p)E_(3−p)  (10)where

X represents hydrogen or an organic group containing an unsaturatedgroup,

q represents an integer of 0 to 10,

D represents a halogen atom, an isocyanate group, or an alkoxyl grouphaving one to three carbon atoms,

E represents hydrogen or an alkyl group having one to three carbonatoms,

n represents an integer of not less than 2 and not more than 25, and

p represents an integer of 1, 2, or 3.

The organic molecules preferably are formed in a monomolecular layer.

Alternatively, a plurality of the monomolecular films may be laminatedon one another by repeating a process for forming the foregoingmonomolecular film a plurality of times, so that a monomolecularbuilt-up film is formed.

In the foregoing chemical formula (B), in the case where X contains anunsaturated group such as a vinyl bond, a hydroxyl group (—OH) can beintroduced by, for instance, projecting an energy beam such as electronbeam or an X-ray beam in an atmosphere containing moisture, and —COOHcan be introduced by immersion in an aqueous solution of potassiumpermanganate. Other methods also are available such as, for instance,the oxygen plasma treatment, the UV/ozone treatment, the coronatreatment, and the treatment by immersion in a mixture solution ofconcentrated sulfuric acid and potassium dichromate (chromium mixed acidsolution treatment). Such a treatment allows an active hydrogen to beintroduced, thereby allowing monomolecular films to be accumulated andbound further.

Further alternatively, after the formation of the monomolecular layerand the tilting (alignment) are repeated alternately, the conductivenetworks may be formed simultaneously in respective monomolecular layersin a monomolecular build-up film in a process for forming the conductivenetwork, so that a conductive monomolecular build-up film is formed.

Alternatively, a series of the monomolecular layer formation, thetilting, and the conductive network formation may be repeated so that aconductive monomolecular build-up film is formed.

A polymerizing method is at least one type selected from electrolyticoxidation polymerization, catalytic polymerization, and energy beampolymerization. Before the formation of the conductive network byelectrolytic oxidation polymerization, preliminary polymerization of atleast one type selected from catalytic polymerization and energy beampolymerization, may be carried out.

The energy beam preferably is at least one selected from ultravioletrays, far-ultraviolet rays, X-rays, and an electric beam.

The energy beam may be at least one selected from polarized ultravioletrays, polarized far-ultraviolet rays, and polarized X-rays, and thetilting and the conductive network formation may be carried outsimultaneously.

As the organic molecule includes a polar functional group, thesensitivity with respect to an electric field applied thereto isenhanced and the response speed is increased, whereby the conductivityof the organic thin film can be varied rapidly. The variation of theconductivity of the organic thin film is considered to be caused in thefollowing manner: upon application of an electric field, a polarfunctional group responds to the electric field, and the structure ofthe conductive network is influenced by the response.

Still further, by doping a charge-transfer-type dopant substance in theconductive network, it is possible to enhance the conductivity further.As the dopant substance, any dopant substance may be used, such asiodine, BF⁻ ion, alkali metals such as Na and K, alkaline earth metalssuch as Ca, etc. Further, other dopant substances may be included, as aresult of being mixed unavoidably due to contamination from tracecomponents contained in a solution used an organic film forming process,from a glass container, and the like.

Since the organic molecules composing a conductive monomolecular layerare in a highly aligned state, consequently conjugate bond chains of theconductive network are present in a specific plane. Therefore, theconductive network formed in the monomolecular layer linearly ranges ina predetermined direction. The linearity of the conductive networkprovides a high conductivity anisotropy. Further, the linearity of theconductive network indicates that conjugate bond chains (conjugatedsystems) composing the conductive network are arrayed substantially inparallel in the same plane within the monomolecular layer. Therefore,the conductive monomolecular layer has a high and uniform conductivity.Furthermore, the linearity of the conductive network causes conjugatebond chains with a high degree of polymerization to be present in amonomolecular layer.

According to the foregoing example, it is possible to provide aconductive monomolecular film and a conductive monomolecular build-upfilm with a significantly enhanced conductivity even if it has a smallfilm thickness.

In the case of a conductive monomolecular build-up film, sinceconductive networks are formed in respective conductive monomolecularlayers, the conductivity of the conductive network of the monomolecularbuild-up film depends on the number of monomolecular films thus stacked.Therefore, it is possible to provide a conductive organic thin filmhaving a desired conductivity by changing the number of the conductivemonomolecular layers composing the film. For instance, in the case of aconductive build-up film obtained by stacking the same conductivemonomolecular layers, the conductivity of the conductive networkincluded therein is substantially proportional to the number of layers.

As long as all the directions of the conductive networks formed in themonomolecular layers are uniform in the conductive monomolecularbuild-up film, the respective tilt angles of aligned organic moleculesin the monomolecular layers may be different from one layer to another.Further, all the monomolecular layers need not be composed of the sameorganic molecules. Still further, the conductive monomolecular build-upfilm may be composed of conductive monomolecular layers in whichrespective types of organic molecules forming the conductivemonomolecular layers are different from one layer to another.

Further, in the case of a conductive monomolecular build-up film, theconductive monomolecular layer closest to the substrate is bound to thesubstrate by chemical bonds, it provides excellent durability such asexcellent spalling resistance.

The tilting direction of organic molecules in the tilting step isdefined as a direction of a line segment obtained by projecting a majoraxis of an organic molecule to a surface of the substrate. Therefore,the tilting angles with respect to the substrate need not be uniform.

In the tilting process, it is possible to tilt an aggregate of organicmolecules composing the monomolecular layer with high accuracy in apredetermined direction. Generally, it is possible to align moleculescomposing a monomolecular layer. Since this provides accurate alignment,it is possible to form a conductive network having a directivity in theconductive network formation easily.

The tilting may be carried out by applying any one of the tilt draining,rubbing, light projection, and alignment utilizing fluctuations ofmolecules in a solution during polymerization, or alternatively, byapplying a plurality of the same in combination by carrying out the samesuccessively. To form a monomolecular film aligned in an accuratelyaligned state by employing different alignment methods in combination, arubbing direction, a polarization direction, and a tilt drainingdirection preferably are made to coincide with one another.

Furthermore, by binding aligned organic molecules in the monomolecularlayer by conjugated bonds, it is possible to form a conductive networkthat has a high degree of polymerization and ranges linearly.Furthermore, with the linearity of the conductive network, it ispossible to form a homogeneous conductive monomolecular layer.

In the foregoing example, a polarized light having a wavelength in arange of visible light is used as the polarized light. According to thisexample, the spalling of the organic molecules composing the organicthin film, and breakdown of the organic thin film due to the breakdownof organic molecules themselves can be prevented or controlled.

According to the foregoing example, in the case where the organic thinfilm is formed on a surface of the substrate having been subjected to arubbing process, the organic molecules composing the organic thin filmexhibit a state of being tilted in a predetermined direction. Generally,a rubbing direction in the rubbing process and a tilting direction ofthe organic molecules of a film formed coincide with each other.

A cloth made of nylon or rayon can be used as a rubbing cloth used inthe rubbing process. As in the configuration described above, the use ofa rubbing cloth made of nylon or rayon is suitable for the purpose ofimproving the accuracy of the alignment.

One or more types of polymerization methods may be applied in theforegoing conductive network formation, so that the molecules composingthe organic thin film are polymerized, or polymerized and linked afterthe polymerization, by conjugated bonds, whereby the conductive networkis formed. In this example, a conductive network that allows forelectric conduction can be formed by binding the polymerizable groups ofthe organic molecules by conjugated bonds. As the polymerization method,at least one selected from electrolytic polymerization, catalyticpolymerization, and energy beam polymerization can be used. Theelectrolytic oxidation polymerization may be carried out in particularat the final step for completing the conductive network, whereby a highconductivity can be obtained.

Furthermore, in the case where each of the molecules forming the organicthin film has a plurality of polymerizable groups that are bound byconjugated bonds, a linking reaction is caused further in a polymerformed by polymerization of the polymerizable groups of one of the twokinds, so that the polymerizable groups of the other kind are bound byconjugated bonds. By so doing, a conductive network having a structuredifferent from that after the polymerization can be formed. Here, thepolymerizable groups of the other kind that are present in side chainsof the polymer formed by the polymerization are linked with one another.

For instance, a monomolecular film is formed with an aggregate oforganic molecules each having a diacetylene group, the monomolecularfilm is subjected to catalytic polymerization, and further, it issubjected to the energy beam polymerization for linking. By so doing, aconductive network including a polyacene-type conjugate system having anextremely high conductivity can be formed.

In the foregoing step of polymerization, the polymerization methodselected from the group consisting of catalytic polymerization,electrolytic polymerization, and energy beam polymerization may beapplied. In this example, a conductive network can be formed by applyingcatalytic polymerization to an organic thin film composed of organicmolecules having polymerizable groups with catalyst polymerizability(hereinafter referred to as catalyst-polymerizable group), by applyingthe electrolytic polymerization to an organic thin film composed oforganic molecules having polymerizable groups with electrolyticpolymerizability (hereinafter referred to as electrolytic-polymerizablegroup), or by applying the energy beam polymerization to an organic thinfilm composed of organic molecules having polymerizable groups that arepolymerized when being irradiated with an energy beam (hereinafterreferred to as energy-beam-polymerizable group). To form a conductivenetwork efficiently, the catalyst polymerization and/or the energy beampolymerization is carried out first, and the reaction is completed byelectrolytic oxidation polymerization at the final stage.

In the case where a set of plural linking steps is employed, it may be acombination of linking steps by different effects, but examples of thesame also include a combination of steps by the same effect underdifferent reaction conditions. For instance, a conductive network may beformed by carrying out a linking step by projecting an energy beam of afirst type after the linking step by the catalyst effect, andthereafter, carrying out a linking step by projecting an energy beam ofa second type.

In the foregoing conductive network formation, the catalyticpolymerization is applied as the polymerization method, and a conductivenetwork is formed in an organic thin film that is formed with anaggregate of organic molecules having pyrrole groups, thienylene groups,acetylene groups, or diacetylene groups, as the polymerizable groups.

For instance, a conductive network including a polypyrrole-typeconjugate system can be formed using organic molecules having pyrrolegroups, and a conductive network including a polythienylene-typeconjugate system can be formed using organic molecules having thienylenegroups.

In the foregoing conductive network forming step, it also is possible toform a conductive network by the energy beam polymerization in theorganic thin film formed with an aggregate of organic molecules havingacetylene groups or diacetylene groups as the polymerizable groups. Inthis example, a conductive network having a polyacetylene-type conjugatesystem can be formed by using organic molecules having acetylene groupsas the organic molecules composing the organic thin film. On the otherhand, a conductive network having a polydiacetylene type conjugatesystem or a polyacene-type conjugate system can be formed by usingorganic molecules having diacetylene groups.

Ultraviolet rays, far-ultraviolet rays, X-rays, or an electric beam maybe used as the foregoing energy beam. In this example, a conductivenetwork can be formed efficiently. Further, since the absorptioncharacteristics are different according to the type of thebeam-irradiation-polymerizable groups, the reaction efficiency can beenhanced by selecting a type of an energy beam and energy that allow forthe improvement of the absorption efficiency. Furthermore, since manybeam irradiation polymerizable groups exhibit absorbing properties withrespect to such energy beams, it is applicable to organic thin filmsformed with organic molecules having various types ofbeam-irradiation-polymerizable groups.

Furthermore, polarized ultraviolet rays, polarized far-ultraviolet rays,or polarized X-rays may be used as the foregoing energy beam, and thetilting step and the conductive network forming step may be carried outsimultaneously. In this example, the organic molecules forming anorganic thin film can be tilted in a predetermined direction (aligned),and the organic molecules can be bound with one another via conjugatedbonds. Therefore, the process can be simplified.

The substrate used in the present invention is made of glass, a resin, ametal, ceramic, etc., and in the case where it has active hydrogen onits surface, it can be used as it is. In the case of a substrate withless active-hydrogen on its surface, the substrate is treated withSiCl₄, HSiCl₃, SiCl₃O—(SiCl₂—O)_(n)—SiCl₃ (where n is an integer of notless than 0 and not more than 6), Si(OCH₃)₄, HSi(OH₃)₃,Si(OCH₃)₃O—(Si(OCH₃)₂—O)_(n)—Si(OCH₃)₃ (where n is an integer of notless than 0 and not more than 6), or the like. These chemical compoundscan be formed by chemisorption, and they preferably are formed so as tohave a film thickness of approximately 1 nm to 10 nm, since such athickness does not impair the transparency. Alternatively, a silica filmor an Al₂O₃ film may be formed thereon by vapor deposition, or activehydrogen may be imparted by activating the substrate surface by coronadischarge, plasma projection, etc.

In the present invention, an organic film memory as a nonvolatile memoryis composed of an organic film as a storage medium, a first linearranged in the vicinity of the organic film for brining the organicfilm into conduction, and a second line arranged in the vicinity of theorganic film for detecting whether the organic film is conductive ornon-conductive.

Further, a memory input/output method is configured in the followingmanner. Organic films are used as storage media, and for each of theorganic films, at least one line for bringing the organic film intoconduction is arranged in the vicinity of the organic film so thatmemory is written by bringing the organic film into conduction using theline. Further, for each of the organic films, at least one line fordetecting the conduction of the organic film is arranged in the vicinityof the organic film so that memory is read.

Further, the substrate of the present invention refers to, apart from anentire substance having insulation surfaces, unless provided otherwise,not only substrates made of insulation materials such as a glasssubstrate, a resin substrate, a resin film, etc., but also substratesmade of semiconductors, metals, etc.

The first or second electric state is maintained by applying apredetermined voltage across the electrodes. For instance, a firstelectric state is maintained by applying a voltage of not lower than +10V, while a second electric state is maintained by applying a voltage ofnot lower than −10 V.

The first or second electric state also can be maintained by passing apredetermined current through the organic film.

The first and second lines may be formed either substantiallyorthogonally with each other or in matrix form.

In a method of the present invention, polymerization preferably iselectrolytic polymerization.

The foregoing linear electric conductors and the organic film may beelectrically continuous via a contact hole that passes therethrough.

The organic film may be extended through the contact hole, and anoutputting operation of the organic film may be carried out by carryinga first current.

Further, the organic film and the first line may be formed on thesubstrate, and insulation films may be formed on at least a part of thefirst line and at least a part of the substrate, while the second linemay be formed so as to cross the first line substantially orthogonally.

Further, a plurality of holes or grooves may be formed in at least apart of the foregoing insulation films.

The following will describe electric behaviors of a preferableconductive organic thin film of the present invention, while referringto FIG. 1. A conductivity of the thin film, for instance, rises up to10³ S/cm in response to a voltage of +10 V applied thereto, and thisstate in which the thin film is maintained is a first electric state.This is a conductive state. Then, in response to a voltage of −10 Vapplied thereto, the conductivity thereof drops to 0 S/cm, and thisstate in which the thin film is maintained is a second electric state.This is a non-conductive state. The threshold value thereof is plottedin a graph with a line in a substantially rectangular form.

As to an application example of the memory, the foregoing memory elementis suitable for use in a memory card or a computer system, as anauxiliary storage medium that does not need backup with use of abattery, since the foregoing memory element stores information evenafter the power is turned off. Further, since it is nonvolatile, it iscapable of functioning as a part of a HDD (hard disk). By using thememory element for the foregoing purposes, the following functions canbe achieved:

(1) enhancing the speed for input/output of memory;

(2) facilitating the higher-density packaging, thereby producinglarge-capacity storage devices at lower cost; and

(3) not losing memory even when the power supply is stopped, therebystably maintaining memory.

EXAMPLES

The following will describe the present invention specifically, whilereferring to examples thereof. In the Examples described below, “%”alone means “percent by mass”.

Example of Synthesis of Chemisorption Molecules

First, a substance expressed by a chemical formula (11) shown below(PEN: 6-pyrrolylhexyl-12,12,12-trichloro-12-siladodecanoate), includinga 1-pyrrolyl group (C₄H₄N—) that is capable of forming a conductivenetwork, an oxycarbonyl group (—OCO—) that is a polar functional group,and a trichlorosilyl group (—SiCl₃) that is dehydrochlorinated withactive hydrogen (for instance, a hydroxyl group (—OH)) on the surface ofthe substrate, was synthesized through steps described below.

I. Method for Synthesizing the Substance (PEN) Expressed by the ChemicalFormula (11)Step 1: Synthesis of 6-bromo-1-(tetrahydropyranyloxy)hexane

197.8 g (1.09 mol) of 6-bromo-1-hexanol was put in a 500-ml reactor andwas cooled to 5° C. or below. 102.1 g (1.21 mol) of dihydropyran wasdropped thereto at a temperature of not higher than 10° C. After thedropping was finished, the mixture was returned to room temperature andstirred for one hour. Residue obtained as a result of the reaction wassubjected to purification by silicagel column with use ofhexane/diisopropyl ether (IPE)=5/1, whereby 263.4 g of6-bromo-1-(tetrahydropyranyloxy)hexane was obtained. The yield of thesame was 90.9%. The reaction of the step 1 is expressed by a formula(12) shown below:Br

CH₂

₆OH→Br

CH₂

₆OTHP  (12)Step 2: Synthesis of N-[6-(tetrahydropyranyloxy)hexyl]pyrrole

38.0 g (0.567 mol) of pyrrole and 200 ml of dehydrated tetrahydrofuran(THF) was put in a 2-liter reactor under flow of argon, and was cooledto 5° C. or below. 354 ml (0.567 mol) of n-butyllithiumhexane solutionof 1.6 M was dropped at 10° C. or below. After the mixture was stirredat the same temperature for one hour, 600 ml of dimethyl sulfoxide wasadded thereto, and THF was removed by heating and distilling, so thatthe solvent replacement was carried out. Next, 165 g (0.623 mol) of6-bromo-1-(tetrahydropyranyloxy)hexane was dropped thereto at roomtemperature. After the dropping, the mixture was stirred at the sametemperature for two hours.

600 mol of water was added to the reaction mixture, and the mixture wassubjected to hexane extraction, so that an organic layer was washed withwater. After drying the same using anhydrous magnesium sulfate, thesolvent was removed by distilling. The residue obtained was subjected topurification by silicagel column with use of hexane/ethyl acetate=4/1,whereby 107.0 g of N-[6-(tetrahydropyranyloxy)hexyl]pyrrole wasobtained. The yield was 75.2%. The reaction of the step 2 is expressedby a formula (13) shown below:

Step 3: Synthesis of N-(6-hydroxyhexyl)-pyrrole

105.0 g (0.418 mol) of N-[6-(tetrahydropyranyloxy)hexyl]pyrrole obtainedas above, 450 ml of methanol, 225 ml of water, and 37.5 ml ofconcentrated hydrochloric acid were put in a 1-liter reactor, and werestirred for six hours at room temperature. The reaction mixture obtainedwas poured into 750 ml of concentrated brine, and was subjected to IPEextraction. An organic layer was washed with concentrated brine. Afterdrying the same using anhydrous magnesium sulfate, the solvent wasremoved by distilling. The residue obtained was subjected topurification by silicagel column with use of n-hexane/ethyl acetate=3/1,whereby 63.1 g of N-(6-hydroxyhexyl)pyrrole was obtained. The yield was90.3%. The reaction of the step 3 is expressed by a formula (14) shownbelow:

Step 4: Synthesis of N-[6-(10-undecenoyloxy)hexyl]-pyrrole

62.0 g (0.371 mol) of N-(6-hydroxyhexyl)-pyrrole, 33.2 g (0.420 mol) ofdry pyridine, and 1850 ml of dry toluene were put in a 2-liter reactor,and 300 ml of a dry toluene solution of 75.7 g (0.373 mol) of10-undecenoylchloride was dropped thereto at 20° C. or below. Thedropping time was 30 minutes. Thereafter, the mixture was stirred at thesame temperature for one hour. The reaction mixture was poured into 1.5liter of iced water, and was made acidic with use of 1N hydrochloricacid. It was subjected to ethyl acetate extraction, an organic layer waswashed with water and concentrated brine and was dried using anhydrousmagnesium sulfate, and the solvent was removed. As a result, 128.2 g ofcrude substance was obtained. This was subjected to purification bysilicagel column with use of n-hexane/acetone=20/1, whereby 99.6 g ofN-[6-(10-undecenoyloxy)hexyl]-pyrrole was obtained. The yield was 80.1%.The reaction of the step 4 is expressed by a reaction formula (15) shownbelow:

Step 5: Synthesis of PEN

2.0 g (6.0×10⁻³ mol) of N-[6-(10-undecenoyloxy)hexyl]-pyrrole, 0.98 g(7.23×10⁻³ mol) of trichlorosilane, and 0.01 g of 5% isopropyl alcoholsolution of H₂PtCl₆-6H₂O were put in a 100-ml pressure-resistant testtube with a cap, and reaction was caused at 100° C. for 12 hours. Afterthe reaction liquid was treated with activated carbon, low-boilingcomponents were removed by distilling under a reduced pressure of2.66×10³ Pa (20 Torr). 2.3 g of PEN was obtained. The yield was 81.7%.The reaction of the step 5 is expressed by a reaction formula (16) shownbelow.

It should be noted that to substitute a trichlorosilyl group at aterminal with a trimethoxysilyl group, PEN expressed by the foregoingchemical formula is stirred with methyl alcohol in an amount three timesthe amount of PEN in molar terms at room temperature, so thatdehydrochlorination occurs. Sodium hydroxide is added thereto asrequired so that the foregoing hydrogen chloride is separated as sodiumchloride.

Regarding PEN obtained, a chart showing a result of the nuclear magneticresonance (NMR) analysis and a chart showing a result of the infrared(IR) absorption spectrum analysis are shown in FIGS. 2 and 3,respectively.

NMR

-   (1) Measuring device: AL300 (device name, manufactured by JEOL,    Ltd.)-   (2) Measuring condition: ¹H-NMR (300 MHz), measuring 30 mg of a    sample in a state of being dissolved in CDCl₃    Infrared Absorption Spectrum: IR-   (1) Measuring device: 270-30 (device name, manufactured by Hitachi,    Ltd.)-   (2) Measuring condition: neat (measuring a sample interposed between    two NaCl plates)

Example 1

First of all, electric characteristics were measured using a basicelement as shown in FIG. 4, to analyze a mechanism of recording.

PEN obtained in the above-described synthesis example was dissolved inpolydimethyl siloxane (silicone oil) as a nonaqueous solvent at aconcentration of 1%, whereby a coating solution was obtained. When thecoating solution was applied over a glass substrate 4,dehydrochlorination occurred at room temperature (25° C.) betweenhydroxyl groups (—OH) on a surface of the glass and chlorosilyl groups(—SiCl₃) of PEN, whereby PEN was bound with the surface of the glass bycovalent bonds. Platinum electrodes 10 were provided by vapor depositionpartially on a surface of an organic film thus obtained. When theorganic film was polymerized electrolytically, any one of the platinumelectrodes 10 was used as a working electrode. As a supportingelectrolyte, for instance, an acetonitrile solution of anhydrous lithiumperchlorate (alternatively, tetraethylammonium tetrafluoroborate, ortetrabutylammonium perchlorate) at a concentration of 0.05 mol/L wasprepared, and the substrate was immersed in the foregoing acetonitrilesolution, while a gold electrode used as a counter electrode and aNaCl-calomel electrode as a reference electrode were immersed thereinalso in the same manner. An electrolytic polymerization reaction wascaused in an inert gas atmosphere (for instance, in helium gas), underthe conditions of a current density of up to 150 μA/cm² and a scanningrate of 100 mV/sec., at room temperature (25° C.), whereby a polypyrrolederivative ultra-thin film 7 was formed on a surface of the substrate.The formation of polypyrrole was confirmed by a Fourier transforminfrared absorption spectroscopy analyzer.

To determine the electric properties of the foregoing organic film,operations of recording, reading, and reproduction were conducted usinga scanning tunneling microscope (STM) and a conductive stylus of anatomic force microscope (AFM). First of all, FIG. 5A is a current imageobtained by determination using the AFM before recording. A platinumelectrode 10 is shown in a left half of the image. In the case of anorganic film 7 that was not subjected to electrolytic polymerization, noflow of current was detected when a stylus was placed at an appropriateposition and a voltage of 0.5 V was applied across the stylus and theplatinum (electrode), and this shows that the organic film 7 was in anon-conductive state (a state of a first conductivity). Thereafter,again, a sample was scanned so that the writing was carried out, with avoltage of 10 V being applied across a stylus 100 and the platinumelectrode 10, and by applying a voltage of 0.5 V across the stylus 100and the platinum electrode 10 over an area including the portion towhich the voltage of 10 V was applied, a current image as shown in FIG.5B was obtained. A difference of FIG. 5B from the FIG. 5A is that theflow of current was detected in a region of the organic film 5 in whichthe writing was carried out (region scanned with a voltage of 10 V beingapplied across the stylus and the platinum). In the region with achanged color in a left half of FIG. 5B, a state of a secondconductivity was detected. A current value was 100 nA. It is consideredthat polymerization occurred due to the application of a voltage of 10V, thereby causing a transition from the non-conductive state to theconductive state. Finally, after a voltage of −10 V was applied acrossthe stylus 100 and the organic film 7, a current image was taken byapplying a voltage of 0.5 V again. An image thus obtained is shown inFIG. 5C. Here, an image showing no flow of current, as at the initialstage, was obtained (the state of the first conductivity).

The organic film was confirmed to be a material that exhibited a memoryeffect (electric memory effect) having a first conductivity as an OFFstate and a second conductivity as an ON state. It was found that,assuming that a bit size of recording is 10 nm, the use of thismechanism ensures even a large capacity recording/reproduction of 10¹²bit/cm². It should be noted that, in both the cases where this organicthin film was a monomolecular film and where it was a build-up filmobtained by laminating monomolecular films, the same effect wasobtained.

Further, the stable ON state (with a conductivity of 1 S/cm or more) andOFF state (with a conductivity of 1×10⁻³ S/cm or less) as shown in FIG.1 was obtained, the switching from the ON state to the OFF stateexhibited a constant threshold voltage of +5 V to +10 V, the switchingfrom the OFF state to the ON state mainly occurred with a voltage ofabout −5 V to −10 V, and a switching speed was such that an ON/OFF ratio(a ratio of a conductivity in the ON state to that in the OFF state) was10¹⁷ to 10² at 1 μsec or less. The threshold voltage of the switchingexhibited a tendency to increase as the film thickness increased. In thecase where an information processing device for performing recording,reproduction, and the like of information by rotating a flat-platerecording medium is prepared by applying the principles of the scanningprobe microscope, a relative speed of the probe to the recording mediumis made constant, whereby the occurrence of resonance upon high-speedscanning and the decrease of a S/N ratio of reproduction signals can beavoided. Therefore, the foregoing device is allowed to become a highlyreliable device that has a large capacity and is capable of high-speedresponse.

Example 2

In this example, first of all, as shown in FIG. 6A, horizontal selectionlines 61 made of a conductive material were formed in a matrix on aglass substrate 64 by coating or the like. In the case where these lineswere, for instance, of the p type, the lines were formed by mixing ap-type impurity during vapor deposition or by accelerated injection of ap-type impurity by injecting, ion doping, etc. after vapor deposition.Examples of the p-type impurity include B, Al, Ga, In, and TL.

Next, a film of an electric insulation material 63 made of SiO₂ (filmthickness: 300 nm) was formed by deposition or coating (FIG. 6B).Thereafter, as shown in FIG. 6C, contact holes 67 were formed in theelectric insulation material 63 as shown in FIG. 6C, and an n-type ionwas injected so that n-type regions 65 were formed as shown in FIG. 6D.Examples of the n-type impurity include N, P, As, Sb, and Bi. It shouldbe noted that in the present example, a rectifier element was formed bya pn junction, but it may be formed by Schottky barrier. Next, verticalselection lines 62 were formed by coating or the like so that theinsulation film 63 prevents the vertical selection lines 62 from beingconnected electrically with the horizontal selection lines 61 (FIG. 6E).Here, the horizontal selection lines 61 and the vertical selection lines62 desirably are formed so as to cross each other orthogonally.

Finally, a conductive monomolecular organic film 66 was formed on thesubstrate with the lines provided in matrix thereon, in the same manneras that in Example 1, as shown in FIG. 6F. Here, as described above, thehorizontal selection lines 61 and the vertical selection lines 62 areconnected with each other via the organic film 66.

As described above, the organic film (monomolecular film) 66 was formedso as to cover, from above, an entirety of the horizontal selectionlines 61 on a lower side, the insulation film 63, and the verticalselection lines 62 on an upper side, which were formed in matrix form.

An organic film (monomolecular film) element thus having across-sectional structure formed as described above is shown in FIG. 7as an example. With the layout in the matrix form as shown in FIG. 7, amultiplicity of layer structures, each of which is composed of thehorizontal selection line 71, the vertical selection line 72, and theconductive organic film 73, are formed two-dimensionally, and eachmemory cell (element employing an organic film) stores one bit. 74denotes a diode, and 75 denotes an ON state.

The recording and reading with respect to each organic film(monomolecular film) element are carried out according to the followingprinciple.

The recording is carried out as follows. Assume that a voltage (or a setcurrent) necessary for making each organic film (monomolecular film)element conductive is X. First, when a voltage (in the forward directionof the rectifier element) of X is applied to each of a horizontalselection line 71 and a vertical selection line 72 in a direction suchthat the same conductivity occurs in an organic film (monomolecularfilm) element in a non-conductive (first conductivity) state (in theforward direction of the pn element), only the organic film(monomolecular film) element present at a crossing point of thehorizontal selection line 71 and the vertical selection line 72 throughwhich current flows is caused to become conductive (second conductivity,the conductivity being not less than 1 S/cm). More specifically, byapplying a predetermined voltage, the conductivity varies from the firstconductivity to the second conductivity. A non-conductive state (firstconductivity, the conductivity being not more than 10⁻³ S/cm) isachieved by changing the polarity of the voltage flowing through thehorizontal selection line and the polarity of the voltage flowingthrough the vertical selection line. The state varies from the secondconductive state to the first conductive state, and a ratio of the firstconductivity to the second conductivity is about 10¹⁷ to 10². Here, thevoltage for achieving the non-conductive state (first conductivity) is−X in the present material system, which is an inverse voltage to thevoltage X for varying the conductivity from the first conductivity tothe second conductivity, but in another material system, it may bedifferent from −X in some cases. The conductivity/non-conductivity ofthe organic film (monomolecular film) element are caused to correspondto 0 and 1, with which one bit of digital signals can be recorded.

When a signal recorded is read out, as in the recording, the horizontalselection lines 71 and the vertical selection lines 72 are used forapplying a voltage (or a current) smaller than X to an organic film(monomolecular film) element to be read. In the case where the organicfilm (monomolecular film) element as a target of the reading operationherein is in the conductive state (second conductivity), a current flowsthrough the organic film (monomolecular film) element, and is outputtedto the vertical selection line 72. In the case where the organic film isin a non-conductive state (first conductivity), less current flowsthrough the vertical selection line 72, and nothing is outputted. Thevertical selection line detects a current and outputs it as readoutdata. It should be noted that when the reading operation is carried outwith respect to the element, recorded contents therein are not damaged,and there is no need to record the same again therein. Therefore, it canbe used as a nonvolatile memory.

It should be noted that Example 2 is described by referring to a case inwhich lower lines and upper lines are formed, but the present inventionis not limited to this case. The same function as that described abovecan be achieved by a configuration composed of vertical selection lines2 and horizontal selection lines made of an electric conductor that arearranged on organic films (monomolecular films) arrayed in a matrix on asubstrate with an electric insulator being interposed therebetween.

Application Example 1

FIG. 8 illustrates an example in which the memory elements 42 of Example2 described above are used in a semiconductor disk substrate 41. 43denotes a connector part. Thus, by using the memory elements 42 in thesemiconductor disk substrate 41, a significantly advantageoussolid-state storage medium that is inexpensive and has a large capacitycan be obtained. Further, the foregoing medium enables the downsizing ofa system as a whole since it does not require a mechanical drivingsystem unlike a conventional diskette or hard disk, and further, it hasa high resistance against shock. Therefore, the medium is suitable as anexternal storage for compact and portable computer systems. Therefore,it can compose a DRAM with a high degree of integration and a largecapacity.

Application Example 2

FIG. 9 is a diagram illustrating a configuration of a computer system200 employing a logic element (microprocessor), a memory element (DRAM),and a semiconductor disk substrate of Examples described above. Thecomputer system 200 is composed of a signal processing part 203, a cachememory 208, a main storage part 201, an external storage part 205, aninput device 213, an output device 214, an input/output control device209, an auxiliary storage device 210 connected with a diskette 211, acommunication port 212 connected with another computer system, etc. Alogic element 204 of Examples described above can be used as the signalprocessing part 203. Further, the element of the foregoing examples canbe sued as the memory element (DRAM) 202 of the main storage part 201.Further, it can be applied to the semiconductor disk substrate 206 andmagnetic disk 207 of the external storage part 205.

With this configuration, a system as a whole can be downsized, and alarge amount of information can be read/written at high speed, wherebythe processing capability of the system as a whole is enhanced.

A DRAM cell of the present example can be used, like a conventional DRAMcell, in electronic devices such as a semiconductor memory card, asemiconductor disk device, a SOI integrated circuit, a microprocessor,and a computer. Particularly, since the DRAM cell of the present examplehas a small size but a large capacity, it ensures the downsizing of asystem as a whole and improves the processing capability.

Example 3

In the present example, an organic film (monomolecular film) 7 wasformed over a substantial entirety of a glass or polyimide filmsubstrate 4 as shown in FIG. 10A. A chemical compound expressed by aformula (17) shown below, for instance, was used as a material for theorganic film. As a coating method for the same, any one of the methodsmay be used among vapor deposition, coating with use of a spin coater, acoating method by immersing the substrate in a solution, etc. Sinceactive hydrogen such as a hydroxyl group is present on a surface of theglass or polyimide film substrate 4, dehydrochlorination ordealcoholization occurred between the foregoing hydrogen and thehalogenated silyl group or alkoxysilyl group of the chemical compound,and residues of the chemical compound were bound by covalent bonds withthe surface of the substrate. Thereafter, washing with a non-aqueoussolution was carried out, and a monomolecular film is obtained.

For instance, 11-(1-pyrrolyl)-undecenyltrichlorosilane expressed by thechemical formula (17) shown below was diluted to 1 percent by mass withdehydrated dimethylsilicone solution, so that a chemisorption liquid wasprepared.

A glass substrate with a thickness of 5 mm was immersed in the foregoingchemisorption liquid so that chemisorption molecules were adsorbed ontosurfaces of the substrate. Thereafter, the glass substrate was immersedin a chloroform solution so that non-reacted film material moleculesremaining thereon were washed and removed. Thus, the monomolecularorganic film 7 expressed by a chemical formula (18) without contaminanton its surface was formed. It should be noted that the chemical formula(18) indicates a case in which all the —SiCl binding groups in thechemisorption molecule react with the surface of the substrate, but atleast one of the —SiCl binding groups may react with the surface of thesubstrate.

Next, a surface of the monomolecular organic film 7 thus formed wassubjected to a rubbing process using a rubbing device normally used forpreparing a liquid crystal alignment film, so that the chemisorptionmolecules composing the monomolecular organic film were aligned. In therubbing process, a 7.0 cm-diameter rubbing roll around which a rubbingcloth made of rayon was wrapped was used, and a rubbing operation wascarried out under conditions of a pressing depth of 0.3 mm, a nip widthof 11.7 mm, the number of revolutions of 1200 per second, and a tablespeed (substrate running speed) of 40 mm/second. Here, a film aligned(tilted) substantially in parallel with the rubbing direction wasobtained.

Next, vapor deposition, photolithography, and etching were carried outso that a pair of 50 mm-long platinum electrodes were formed with a gapof 5 mm therebetween on the surface of the monomolecular film by vapordeposition, and thereafter, electrolytic oxidation polymerization wascarried out by immersing the substrate in ultrapure water at roomtemperature while a voltage of 8 V was applied across the pair ofplatinum electrodes for 6 hours. Thus, a conductive region having aconductive network that included a conductive polypyrrole typeconjugated system ranging in a predetermined direction (rubbingdirection), which had as a polymerization unit the structure expressedby a chemical formula (19) shown below, was formed between the platinumelectrodes.

The organic conductive film obtained had a thickness of approximately2.0 nm, and a thickness of a polypyrrole portion thereof wasapproximately 0.2 nm.

A current of 1 mA was caused to flow by application of a voltage of 8 Vacross the foregoing platinum electrodes via the foregoing organicconductive film. Therefore, a monomolecular film having a conductiveregion with a conductive network having a conductivity of approximately10³ S/cm was obtained, without doping an impurity such as a donor or anacceptor.

Before the foregoing electrolytic polymerization, platinum was depositedon a portion of the foregoing thin film by vapor deposition (so as tohave a film thickness of 1 μm), so that it functions as a workingelectrode. For instance, an acetonitrile solution of anhydrous lithiumperchlorate (alternatively, tetraethylammonium tetrafluoroborate, ortetrabutylammonium perchlorate) at a concentration of 0.05 mol/L wasprepared as an electrolytic solution, and the foregoing thin filmsubstrate 4 was immersed in the acetonitrile solution, while goldelectrodes as paired electrodes and NaCl-calomel electrodes as referenceelectrodes were also immersed therein. Polymerization was carried outunder conditions of an inert ambient gas (for instance, helium gas), acurrent density of approximately 150 μA/cm², and a scanning speed of 100mV per second, so that a polypyrrole derivative thin film 7 was formedon the surface of the substrate. The formation of the polypyrrolederivative thin film was confirmed by Fourier transform infraredspectroscopy.

Next, when lines in matrix form were prepared, only those in an Xdirection were prepared first, for convenience (FIG. 10B). These linesare referred to as vertical selection lines 1. The vertical selectionlines 1 were formed by forming Si by vapor deposition, plating or thelike, so that the lines had a thickness of 0.5 μm. Since the linesdesirably were n type, an n-type impurity (for instance, phosphor (P),arsenic (As), or antimony (Sb)) may be mixed during vapor deposition, oralternatively, an n-type impurity may be injected after vapordeposition, or subjected to accelerated injection by ion doping, etc.

Then, lines 2 with substantially the same thickness were formed on thevertical selection lines 1 so as to be arrayed in the same pattern (FIG.10C). An impurity (for instance, boron (B), aluminum (Al), gallium (Ga),or indium (In)) was mixed therein by the same method as that describedabove so that they had a characteristic of p type, in contrast to theforegoing n type. For convenience of description, the n-type and p-typelines are referred to as vertical selection lines 8.

Since the vertical selection lines 8 had pn junction in the verticaldirection, current flowed only in one direction. In other words, hereinthe lines were formed so that the configuration of a pn junction wasprepared, but the junction may be Schottky barrier.

Thereafter, an insulation material film 3 (film thickness: 300 nm) suchas SiO₂ was formed by deposition or coating (FIG. 10D). Then, contactholes 9 with a diameter of 2 μm each were formed so that the organicfilms were exposed (FIG. 10E). Here, an insulation material 3 such asSiO₂ may be deposited by vapor deposition using a metal mask so that theorganic films are exposed. Or alternatively, photolithography may becarried out preliminarily, and an insulation film may be formed by thelift-off method or the like.

Then, platinum films 5 were formed by deposition or coating so as tohave a thickness of 5 μm, as horizontal selection lines (FIG. 10F).

Next, an insulation material film 13 of SiO₂ (film thickness: 300 nm)was formed by deposition or coating (FIG. 11A).

Then, an organic film 17 composed of a polypyrrole derivative film wasformed in the same manner as that described above (FIG. 11B).

Next, in the same manner as that shown in FIGS. 10B to 10F, verticalselection lines 11 were formed, and lines 12 also were formed on thevertical selection lines 11 in the same pattern so as to have the samethickness (FIG. 11C), which are referred to as vertical selection lines18. Since the vertical selection lines 8 had pn junction in the verticaldirection, current flowed only in one direction. In other words, hereinthe lines were formed so that the configuration of a pn junction wasprepared, but the junction may be Schottky barrier.

Thereafter, an insulation material film 13 (film thickness: 300 nm) suchas SiO₂ was formed by deposition or coating, contact holes (via holes)19 with a diameter of 2 μm each were formed so that the organic filmswere exposed, and horizontal selection lines 15 were formed bydeposition or coating (FIG. 10D).

Thus, by successively forming the horizontal selection lines, and then,the insulation film, and thereafter forming the vertical selectionlines, a memory cell or a nonvolatile memory with a three-dimensionalstructure can be prepared, and their capacity can be increased easily.

An example of an organic film (monomolecular film) nonvolatile storageelement having the cross-sectional structure formed as described aboveis shown in FIG. 7. With the layout in the matrix form as shown in FIG.7, a multiplicity of layer structures, each of which is composed of thehorizontal selection line, the vertical selection line, and theinsulation material, are formed three-dimensionally, and the organicfilm (monomolecular film) in each structure (memory cell) stores onebit. The storage and read out with respect to each organic film(monomolecular film) are carried out according to the followingprinciples.

First, the recording method is described. An initial state of theorganic film is referred to a first electric state exhibiting a firstresistance. By applying a voltage of not lower than −X (for instance,−10 V) as a first threshold voltage shown in FIG. 1, which is necessaryfor making each organic film (monomolecular film) conductive, to eachorganic film (monomolecular film) storage element, the organic filmmakes a transition to a second electric state exhibiting a secondresistance. Thus, by making a transition to an organic film having alower resistance as compared with the initial stage, the organic filmbecomes conductive. In other words, by applying voltage satisfying X toone of the vertical selection lines and one of the horizontal selectionlines, an organic film present at a crossing point of the selectionlines through which current flows becomes conductive, and the recordingis completed. The conductive state (the second electric state exhibitingthe second resistance) has no change in its characteristics unless asecond threshold voltage (for instance, not less than 10 V) that causesfrom the second electric state to the first electric state is appliedthereto. As to the reading, current flows through a portion (organicfilm) subjected to recording, thereby reaching output and being readout. Even if current flows through a portion not having been subjectedto recording, nothing is outputted to the vertical selection line 2. Byapplying the second threshold voltage contrarily, an organic filmbecomes non-conductive, thereby preventing data to be outputtedtherefrom from being outputted, which enables erasure of the data.

To observe the foregoing phenomenon, operations of recording, reading,and reproduction were experimented using a scanning tunneling microscope(STM) and a conductive stylus of an atomic force microscope (AFM), inthe same manner as that in Example 1. Consequently, the results shown inFIGS. 5A to 5C were obtained as in Example 1.

Thus, the stable ON state (with a resistance of 10 Ω) and OFF state(with a resistance of not less than M Ω) was obtained, the switchingfrom the ON state to the OFF state exhibited a constant thresholdvoltage of +5 V to +10 V, the switching from the OFF state to the ONstate mainly occurred with a voltage of −5 V to −10 V, and a switchingspeed was such that an ON/OFF ratio (a ratio of a conductivity in the ONstate to that in the OFF state) was in a not less than five-digit orderat 1 μsec or less. The threshold voltage of the switching exhibited atendency to increase as the film thickness increased. In the case wherean information processing device for performing recording, reproduction,and the like of information by rotating a flat-plate recording medium isprepared by applying the principles of the scanning probe microscope, arelative speed of the probe to the recording medium is made constant,whereby the occurrence of resonance upon high-speed scanning and thedecrease of a S/N ratio of reproduction signals can be avoided.Therefore, the foregoing device is allowed to become a highly reliabledevice that has a large capacity and is capable of high-speed response.

By changing the polarity of the voltage applied to each selection line,and applying the second threshold voltage for changing the state fromthe second electric state to the first electric state, the state of theorganic film can be caused to make a transition from the conductivestate to the non-conductive state. The conductivity and non-conductivityof the organic film (monomolecular film) are made to correspond to 0 and1, whereby one bit of digital signals can be recorded.

The vertical selection lines detect current, which are readout data. Itshould be noted that when the reading operation is carried out withrespect to the block element, recorded contents therein are not damaged,and there is no need to record the same therein again. Therefore, it canbe used as a nonvolatile memory.

An experiment was carried out to determine to what degree the organicfilm is degraded, during 10¹⁵ cycles in one month, in which therecording, reproduction, erase, and reproduction in the stated ordercompose one cycle. As a result, no particular deterioration wasobserved. Further, signals were read out with sufficient S/N at alltimes during the experiment, and no degradation of characteristics wasobserved in repetitive recording and reproduction.

Example 4

First, electric characteristics were measured using an element as shownin FIGS. 12A and 12B, to determine the mechanism of recording.

Platinum was deposited by vapor deposition so as to have a thickness of0.5 μm, a width of 1 μm, and a length of 5 μm on a substrate 101 made ofa polyimide film having a thickness of 1000 μm, and this was used as agate electrode 102. Next, a silica film (SiO₂) was formed by vapordeposition so as to have a thickness of 1 μm. This was used as a gateoxide film 103.

Next, a source electrode 104 and a drain electrode 106 were formed withplatinum by vapor deposition so that each of them had a thickness of 1μm, a width of 1 μm, and a length of 5 mm, while at the same timeplatinum was deposited by vapor deposition so as to have a thickness of2 μm, a width of 1 μm, and a length of 5 mm, as a contact part 107. Adistance between the contact part 107 and the source electrode 104 was30 μm, and a distance between the source electrode 104 and the drainelectrode 106 was 5 μm. Finally, after an electric insulation film 111was formed, a portion of the contact electrode 107 was subjected to dryetching so that holes were formed, and horizontal selection lines 112were formed.

A chemisorption liquid was prepared using PEN of the foregoing synthesisexample and diluting it with a dehydrated dimethyl silicone solvent to 1wt %. The chemisorption liquid was coated on spaces between the contactpart 107 and the source electrode 104, and between the source electrode104 and the drain electrode 106, so that a chemisorption reaction wascaused. Further, non-reacted portions of the foregoing substance, whichremained on a surface thereof, were removed by washing with chloroform,whereby a monomolecular film was formed (FIG. 13). Since many hydroxylgroups containing active hydrogen are present in the gate oxide film 103made of silica, dehydrochlorination of —SiCl₃ groups of the PEN with thehydroxyl groups occurred, and a monomolecular film 163 a composed ofmolecules expressed by a chemical formula (20) below was formed, whichwas bound with the surface of the substrate by covalent bonds.

Method for Aligning the Molecular Film

Next, the substrate with the monomolecular film 163 a formed thereon waswashed with a non-aqueous chloroform solution, and after drying thesame, a rubbing alignment process as shown in FIG. 28A was carried out,whereby a monomolecular film 163 b thus aligned, shown in FIG. 14, wasformed.

Here, the alignment process is described in detail. FIGS. 28A to 28C areschematic perspective views illustrating alignment methods for tilting(aligning) molecules composing an organic thin film. FIG. 28Aillustrates a rubbing alignment process, FIG. 28B illustrates an opticalalignment process, and FIG. 28C illustrates a draining alignmentprocess.

The rubbing alignment process is a process for aligning organicmolecules composing a monomolecular film 304 in a rubbing direction B byrubbing a surface of the monomolecular film 304 with a rubbing cloth341, by rotating, in a rotation direction A, a rubbing roll 342 wrappedwith the rubbing cloth 341 that is in contact with the monomolecularfilm 304, while transporting a substrate 301 with the monomolecular film304 formed thereon in a predetermined direction (substrate transportingdirection) C, as shown in FIG. 28A. By so doing, the monomolecular film304 aligned in the rubbing direction B can be formed on the substrate301.

The optical aligning process is a process of projecting eitherultraviolet rays or visible rays 345 to a polarizing plate 343 having atransmission axis direction D, as shown in FIG. 28B, so as to alignorganic molecules composing a monomolecular film 304 in a polarizationdirection E with a polarized light 346. As the polarized light, linearlypolarized light is preferable. By so doing, the monomolecular film 304aligned in the polarization direction can be formed on the substrate301.

The draining alignment process is a process of lifting up a substrate301 in a lifting direction F, while tilting the same at a predeterminedtilt angle with respect to a liquid level of an organic solvent 144 forwashing as shown in FIG. 28C, so that the organic molecules composingthe monomolecular film 304 are aligned in a direction G in which thesolvent is drained. By so doing, the aligned monomolecular film 304 canbe formed on the substrate 301.

Though not shown in the drawings, the alignment can be achieved byfluctuations of molecules in a solution during the catalyticpolymerization or the electrolytic oxidation polymerization.

Polymerization Process

Next, electrolytic polymerization was carried out. The platinumelectrodes 104 and 106, for instance, were used working electrodes (FIG.15), and an acetonitrile solution of anhydrous lithium perchlorate(alternatively, tetraethylammonium tetrafluoroborate, ortetrabutylammonium perchlorate) at a concentration of 0.05 mol/L wasprepared, for instance, as an electrolytic solution, and the substratewas immersed in the foregoing acetonitrile solution. An electrolyticpolymerization reaction was caused in an inert gas atmosphere (forinstance, in helium gas), at room temperature (25° C.), under theconditions of a current density of up to 150 μA/cm² and a scanning rateof 100 mV per second, whereby a polypyrrole derivative conductive thinfilm 108 was formed on a surface of the substrate (FIGS. 12A and 15).The formation of polypyrrole was confirmed with Fourier transforminfrared absorption spectroscopy analyzer.

In electrolytic oxidation polymerization, conjugated bonds areself-organized in the direction of the electric field. Therefore, whenthe polymerization was completed, the completion can be confirmed by thefirst electrode 104 and the second electrode 106 being connectedelectrically with each other via the conductive polymer film 108. Theorganic conductive film 108 obtained had a thickness of approximately2.0 nm, a thickness of a polypyrrole portion thereof was approximately0.2 nm, and an organic conductive film 34C had a length of 1 μm and awidth of 5 μm. Using the foregoing configuration, electrolytic oxidationpolymerization was conducted, using the first electrode 104 (sourceelectrode) as a positive electrode, and the second electrode 106 (drainelectrode) as a ground (earth). The manner of application of theelectric field relates to the “directivity” of a conductive memory to beformed later.

One unit of the organic conductive film polymer obtained is expressed bya chemical formula (21) shown below:

Next, as shown in FIG. 12A, a silica film (SiO₂) was formed by vapordeposition so as to have a thickness of 1 μm, as an electric insulationfilm 111. Next, platinum was deposited by vapor deposition so that eachhad a thickness of 0.5 μm, a width of 1 μm, and a length of 5 mm, ashorizontal selection lines 112. A cross-sectional view of a deviceobtained is shown in FIG. 12A, and a principal part perspective view ofa memory part thereof is shown in FIG. 12B. 113 in FIG. 12A denotes atransistor part as a principal part of a non-volatile memory, 104 a to104 d in FIG. 12B denote source electrodes, 106 a to 106 d thereindenote drain electrodes (vertical selection lines), 107 denotes each ofcontact electrodes connected with the horizontal selection lines 112 ato 112 d, and 108 and 110 denote conductive organic thin films.

Measurement

It was determined by an atomic force microscope (AFM) available in themarket (SAP 3800N, manufactured by Seiko Instruments Inc.) in theAFM-CITS mode that the obtained conductive organic film 108 withoutdoping had a conductivity ρ of more than 1×10⁷ S/cm at room temperature(25° C.) under conditions of a voltage of 1 mV and an amperage of 160nA. This was because the foregoing ammeter was only capable ofdetermining up to 1×10⁷ S/cm, and in the foregoing case, it wasoff-scale. Considering that gold and silver as metals having excellentconductivities have 5.2×10⁵ S/cm and 5.4×10⁵ S/cm, respectively, at roomtemperature (25° C.), the conductivity ρ of the organic conductive filmof the present example is surprisingly high. Therefore, the organicconductive film of the present invention can be regarded as“superconducting metal film”.

In the present invention, it is easy to decrease the conductivity ρ ofthe organic conductive film, since this can be accomplished by providingthe conductive network incompletely, or by decreasing the alignmentdegree of molecules.

FIG. 16 is an enlarged view of a part of the conductive organic thinfilm 108 between the source electrode 104 and the drain electrode 106 inFIGS. 12A and 12B.

By such a method, the readout of the recorded information, and thereproduction of the same were conducted using the organic thin filmsample having metal electrodes as shown in FIGS. 12A and 12B, and aconductive AFM probe.

Consequently, the results shown in FIGS. 5A to 5C for Example 1 wereobtained.

Thus, the stable ON state (with a conductivity of 1 S/cm or more) andOFF state (with a conductivity of 1×10⁻³ S/cm or less) as describedabove were obtained, the switching from the ON state to the OFF stateexhibited a constant threshold voltage of +5 V to +10 V, the switchingfrom the OFF state to the ON state mainly occurred with a voltage ofabout −5 V to −10 V, and a switching speed was such that an ON/OFF ratio(a ratio of a conductivity in the ON state to that in the OFF state) was10¹⁷ to 10² at 1 μsec or less. The threshold voltage of the switchingexhibited a tendency to increase as the film thickness increased. In thecase where an information processing device for performing recording,reproduction, and the like of information by rotating a flat-platerecording medium is prepared by applying the principles of the scanningprobe microscope, a relative speed of the probe to the recording mediumis made constant, whereby the occurrence of resonance upon high-speedscanning and the decrease of a S/N ratio of reproduction signals can beavoided. Therefore, the foregoing device is allowed to become a highlyreliable device that has a large capacity and is capable of high-speedresponse.

Next, a wiring diagram of a nonvolatile memory according to the presentexample is described, with reference to FIG. 17. 156 a to 156 d denoteconductive organic thin films, 155 denotes a MOS transistor, 150 denotesvertical-direction current flowing through bit lines (vertical selectionlines 106 a to 106 e), 152 denotes current flowing through word lines(horizontal selection lines 112 a to 112 c), 151 denotes a bit linecontrol circuit, and 153 denotes a word line control circuit. BL denotesa bit line (source electrode), while WL denotes a word line (horizontalselection line). Ends on one side of the conductive organic thin films156 a to 156 d are connected with ends on one side of the MOStransistors 155, while ends on the other side of the conductive organicthin films 156 a to 156 d are connected with the word lines WL.

Upon polymerization, the vertical selection lines 106 a to 106 e aregrounded (earthed), while a high voltage, which is positive, is appliedto the source electrode lines 104 in FIG. 12A. Further, when a positivevoltage is applied to the source electrode lines 104, the contact parts107 (word lines of the horizontal selection lines 112 a to 112 c) aregrounded. When this polymerization process is carried out, the SiO₂ film111 may be formed beforehand. The polymerization may be carried out byusing the source electrodes 104 a to 104 c as grounds and applying apositive voltage to the contact parts 107 and the vertical selectionlines 106 a to 106 e. As to the polymerization environment, thepolymerization may be carried out in water, or in the air. Thepolymerization is completed earlier if light is projected to the organicthin films during the polymerization.

Thereafter, the SiO₂ film 111 is formed, contact holes are formed by dryetching, and the horizontal selection lines 112 a to 112 c (word lines)shown in FIG. 17 are formed with a metal or the like.

With the present embodiment, a delay time occurring to the readout ofinformation can be controlled to a nsec order. Therefore, it is possibleto provide a memory from which information can be read out at a highspeed.

For instance, when cells of the conductive organic thin films 156 a and156 d are in an ON state (current flowing, already polymerized), sincethe cell of the conductive organic thin film 156 a is in the ON state,the application of a voltage to the horizontal selection lines 112 acauses a voltage to be applied to the gate electrodes G154 a therebyturning the MOS transistor 155 on. This causes a current 150 to flow thebit line, thereby reaching the output. As a result, it is determinedthat the cell of the conductive organic thin film 156 a is in the ONstate (current flowing), and a bit of 1 is provided (reproduced state).

Here, when an inversed voltage (−X[V]) is applied across the word lineof the horizontal selection line 112 a and the source electrode line104, the state makes a transition to a state in which current does notflow. In other words, even if a voltage is applied to the horizontalselection line 112 a so that a voltage is applied to the gate electrodeG154 a to turn on the switch of the MOS transistor 155 as in theforegoing case, the current 150 is not generated in the bit line.Therefore, no current reaches the output, and a bit of 0 is provided. Inother words, by treating an organic film as a variable resistor, theconfiguration can be treated as a nonvolatile memory. The MOS transistor155 preferably is provided for preventing leakage current.

A ratio between the second and first conductivities of the organic filmelement preferably is large. The reason is that since there aredifferences in threshold voltages and gains of MOS transistors, it isdesirable to use the organic film element having a large conductivityratio, in order to identify information contents in the memory cellprecisely.

Next, an operation is described, with reference to FIG. 18. Here, apolymerization method without source electrode lines is described. Whenthe polymerization is carried out, the bit lines (106 a to 106 e in FIG.12A) are set so as to have approximately 5 V, a voltage of approximately10 V is applied to word lines (horizontal selection lines 112 a to 112 cin FIG. 12A). Here, when a voltage of 20 V is applied to the gateelectrodes Vg, a current of approximately 1 mA flows through the MOStransistors. Using this constant current, organic film elements can bepolymerized (Write Operation, first from the left side in FIG. 18). Toconduct this polymerization step, the SiO₂ film 111 desirably is formedbefore the film formation. As to the polymerization environment, thepolymerization may be carried out in water, or in the air. Thepolymerization is completed earlier if light is projected to the organicthin films during the polymerization.

Next, a method for reproducing organic film elements (cells) in whichthe polymerization is completed is described. The bit lines (106 in FIG.12A) are set to have approximately 0 V, and a voltage of approximately 3V is applied to the word lines (horizontal selection lines). Here, whena voltage of approximately 10 V is applied to the gate electrodes, acurrent of approximately 0.05 mA flows through the MOS transistors. Thiscauses a current to flow through the organic film elements, which leadto outputs to the bit lines (Read Operation, second from the left sidein FIG. 18).

Next, after a strong electric field in an inversed direction is appliedby flowing a current through the organic films in a direction inversedto the current flow during the previous polymerization, a state in whichno current is allowed to flow can be achieved. More specifically, thebit lines (106 in FIG. 12A) are set to have approximately −5 V, and avoltage of approximately −10 V is applied to the word lines (horizontalselection lines 112). Here, when a voltage of 20 V is applied to thegate electrodes 102, a current of approximately −1 mA flows through theMOS transistors. This causes a state in which no current is allowed toflow through the organic film elements utilizing the foregoing constantcurrent (Erase Operation, third from the left side in FIG. 18).

Once the state in which no current is allowed to flow is created, evenif the respective voltages in FIG. 18, second from the left, areapplied, zero current flows through the bit lines, and no output isobtained, whereby a bit of 0 is obtained (Read Operation, first on theright side in FIG. 18). Thus, without the lines 104, it is possible toconduct the polymerization utilizing a constant current, or to create astate in which no current is allowed to flow.

Example 5

Device structures shown in FIGS. 19 to 27 may be formed as appliedexamples of Example 4.

First, as shown in FIG. 19, gate electrodes 102 are formed with aconductive material on a substrate 101. The material may be a metalmaterial with a high conductivity, such as gold, silver, copper,platinum, or tungsten. Subsequently, an insulation film made of SiO₂ orthe like is formed so as to have a thickness of 50 nm. Then, on asurface of the SiO₂ film 103 thus formed, source electrodes 104 anddrain electrodes 106 are formed by metal mask or photolithography.

Next, conductive organic films are formed by adsorption on portionswhere SiO₂ is exposed, other than the drain electrodes 106 and thesource electrodes 104. Thereafter, an insulation film 103 such as SiO₂is formed so as to have a thickness of 100 nm in the same manner.Subsequently, etching is carried out to a depth of approximately 100 nm,i.e., to the conductive organic films thus formed, by using a dryetching device. This etching is intended to provide holes as contactholes 107 for connection with horizontal selection lines 112 formed byvapor deposition via the foregoing organic films. After the contactholes are formed, the horizontal selection lines 112 are formed bycoating, vapor deposition, or the like. Here, it is desirable that thehorizontal selection lines 112 are formed so as to cross the sourceelectrodes 104 and the drain electrodes 106 substantially orthogonally.

As the conductive organic films (monomolecular films) 108 and 110, thinfilms may be used that are composed of chemisorption moleculescontaining conjugate groups selected from, for instance, thosefunctioning in forming polyacethylene, polydiacetylene, polyacene,polypyrrole, and polythienylene, and functional groups that can be boundwith a surface of a substrate by covalent bonds.

It should be noted that an alkyl group with an appropriate length may beintroduced in a pyrrolyl group or a thienyl group, and further, a polarfunctional group, for instance, an oxycarbonyl group, may be introducedbetween a pyrrolyl group or thienyl group and silicon. An ethynyl groupmay be used if it can be bound by a conjugate bond. Alternatively, otherthan those materials, materials whose molecule has a chemical structurehaving at least a part with a π electronic level as an electronic stateor a part with a σ electronic level as an electronic state may be used.Examples of an applicable coating method include vapor deposition,coating with a spin coater, coating by a sol-gel process, and coating byimmersion in a solution. Further, the organic films thus coated may bealigned by a rubbing process. As an aligning method other than therubbing process, a polarized light may be projected to the organic filmsthat are configured so as to have a photoresponsive functional group,whereby organic films may be aligned in the polarization direction.Alternatively, as another aligning method, when the coating is carriedout by immersion in a solution, the substrate may be lifted up whilebeing tilted at a predetermined tilt angle with respect to a liquidlevel thereof, whereby the organic films are aligned in the drainingdirection. In the organic films, optionally, conjugate-bondable portionsthereof may be polymerized by catalytic polymerization, electrolyticpolymerization, or energy beam polymerization with X rays, electronbeams, UV rays or the like. Thereafter, after laminating an insulationfilm 103, horizontal selection lines 112, an insulation film 103, andsource electrodes 104 may be formed further successively, whereby memorycells, or a nonvolatile memory, having a three-dimensional structure canbe produced.

FIG. 20 shows an example in which the conductive organic thin films ofExample 4 described above are formed on an insulation film 103, on whichcontact electrodes 107, source electrodes 104, and drain electrodes 106are formed further.

FIGS. 21 and 22 show examples in which gate electrodes 102 are formedabove source electrodes 104 and drain electrodes 106.

FIGS. 23 and 24 show examples in which contact electrodes 107, sourceelectrodes 104, drain electrodes 106, and conductive organic thin films108 and 110 are formed in a top part.

FIGS. 25 and 26 show examples in which gate electrodes 102 are formed ona top part.

FIG. 27 shows an example in which gate electrodes 102 are formed on asubstrate 1, an insulation film 103 is formed thereon, contactelectrodes 107, source electrodes 104, and drain electrodes 106 areformed thereon, conductive organic thin films 108 and 110 are formedthereon, an insulation film 111 is formed thereon, and horizontalselection lines are formed thereon; likewise, gate electrodes 122 areformed on a substrate 121, an insulation film 123 is formed thereon,contact electrodes 127, source electrodes 124, and drain electrodes 126are formed thereon, conductive organic thin films 128 and 130 are formedthereon, an insulation film 131 is formed thereon, and horizontalselection lines 132 are formed thereon; and these are laminated via anintermediate layer 133 so as to form a laminate structure. The structureis not limited to the two-layer structure, and a multilayer structurehaving not less than two layers can be formed.

Example 6

Through a synthetic process described above,{6-[(3-thienyl)hexyl-12,12,12-trichloro-12-siladodecanoate]} (TEN)expressed by a chemical formula (22) shown below was synthesized.

Organic films were formed in the same manner as that in Example 1 usingthe foregoing compound. Polythienyl-type organic conductive filmsobtained are expressed by a chemical formula (23) shown below.

To observe the foregoing phenomenon, operations of recording, reading,and reproduction were experimented using a scanning tunneling microscope(STM) and a conductive stylus of an atomic force microscope (AFT), inthe same manner as that of Example 1. Consequently, the results shown inFIGS. 5A to 5C were obtained as in Example 1.

Further, the stable ON state (with a conductivity of 1 S/cm or more) andOFF state (with a conductivity of 1×10⁻³ S/cm or less) as shown in FIG.1 was obtained, the switching from the ON state to the OFF stateexhibited a constant threshold voltage of +5 V to +10 V, the switchingfrom the OFF state to the ON state mainly occurred with a voltage ofabout −5 V to −10 V, and a switching speed was such that an ON/OFF ratio(a ratio of a conductivity in the ON state to that in the OFF state) was10¹⁷ to 10² at 1 μsec or less.

Example 7

Whether or not the conductive molecules were aligned or not in Examples1 to 6 was checked by, as shown in FIG. 29, forming a liquid crystalcell 170, interposing the same between polarizing plates 177 and 178,projecting light thereto from a back side thereof, and observing thesame at a position 180. The liquid crystal cell 170 was prepared byholding glass plates 171 and 173 provided with conductive molecularfilms 172 and 174, respectively, in a manner such that the conductivemolecular films were disposed on inner sides with a gap distance of 5 to6 μm therebetween, sealing the periphery thereof with an adhesive 175,and injecting a liquid crystal composition 176 (nematic liquid crystal,for instance, LC, MT-5087LA manufactured by CHISSO CORPORATION) into thegap.

(1) In the case where the polarizing plates 177 and 178 are placed sothat their polarizing directions cross each other, alignment directionsof the conductive molecular films 172 and 174 are directed in the samedirection, and the polarizing direction of one of the polarizing plateis made parallel with the alignment direction, while the polarizingdirection of the other polarizing plate is made orthogonal to thealignment direction. If the molecules are aligned completely, the liquidcrystal is aligned, whereby a uniform black color is obtained. If auniform black color is not obtained, it implies an alignment defect.

(2) In the case where the polarizing plates 177 and 178 are placed sothat their polarizing directions are parallel with each other, alignmentdirections of the conductive molecular films 172 and 174 are directed inthe same direction, and the polarizing directions of both of thepolarizing plate are made parallel with the alignment direction. If themolecules are aligned completely, the liquid crystal is aligned, wherebya uniform white color is obtained. If a uniform black color is notobtained, it implies an alignment defect.

It should be noted that in the case where a substrate on the back sideis not transparent, only one polarizing plate is arranged on an upperside, and light is projected from a front side thereof, so thatobservation is carried out using reflected light.

By these methods, it was confirmed that the conductive molecular filmsobtained in Examples 1 to 5 were aligned.

Industrial Applicability

As has been described above so far, the present invention not onlyallows writing/reading of record to be performed utilizing a change inan electrical resistance, but also enables dense packaging.

1. A nonvolatile memory comprising: at least a first electrode and a second electrode provided on a substrate, the first and second electrodes being separated from each other; and a conductive organic thin film for electrically connecting the first and second electrodes, wherein the conductive organic thin film has a first electric state in which it exhibits a first resistance, and a second electric state in which it exhibits a second resistance, a first threshold voltage for a transition from the first electric state to the second electric state, and a second threshold voltage for a transition from the second electric state to the first electric state are different from each other, either the first electric state or the second electric state is maintained at a voltage in a range between the first threshold voltage and the second threshold voltage, the conductive organic thin film is formed with organic molecules, each of which includes: a terminal binding group that is bound with a surface of the substrate or a surface of an insulation layer on the substrate by a covalent bond; and a conjugate group, and, each conjugate group is polymerized with another conjugate group of another organic molecule so as to form the conductive organic thin film.
 2. The nonvolatile memory according to claim 1, wherein the first or second electric state is maintained by applying a predetermined voltage across the electrodes.
 3. The nonvolatile memory according to claim 1, wherein the first or second electric state also can be maintained by passing a predetermined current through the conductive organic thin film.
 4. The nonvolatile memory according to claim 1, wherein the first and second electrodes may be formed either substantially orthogonally with other or in matrix form.
 5. The nonvolatile memory according to claim 1, wherein the conjugate group of the conductive organic thin film is at least one conjugate group selected from conjugate groups that function in forming polypyrrole, polythienylene, polyacethylene, polydiacetylene, and polyacene.
 6. The nonvolatile memory according to claim 1, wherein the terminal binding group of the conductive organic thin film forms at least one type of bond selected from a siloxane-type (—SiO—) bond and a SiN— type bond where Si and N may have other binding groups equivalent to their valences.
 7. The nonvolatile memory according to claim 1, wherein the conductive organic thin film is aligned.
 8. The nonvolatile memory according to claim 1, wherein a molecular unit composing the conductive organic thin film is expressed by a chemical formula (A) given as:

where B represents hydrogen, an organic group including an alkyl group having one to ten carbon atoms, an active hydrogen introducible group, or its residue, A represents at least one conjugate bond selected from a pyrrole group, a thienylene group, an acetylene group, and a diacetylene group, Z represents at least one functional group selected from an ester group (—COO—), an oxycarbonyl group (—OCO—), a carbonyl group (—CO—), a carbonate group (—OCOO—), and an azo group (—N═N—), or a chemical bond (—), m and n represent integers satisfying 2≦m+n≦25, Y represents oxygen (O) or nitrogen (N), E represents hydrogen or an alkyl group having one to three carbon atoms, and p represents an integer of 1, 2, or
 3. 9. The nonvolatile memory according to claim 1, wherein the conductive organic thin film is connected with a diode.
 10. The nonvolatile memory according to claim 9, wherein the diode is a PN junction film.
 11. The nonvolatile memory according to claim 1, wherein a ratio of a first conductivity in the second electric state to a second conductivity in the first electric state is 10² to 10¹⁷.
 12. The nonvolatile memory according to claim 1, wherein the first electrode is a source electrode and the second electrode is a drain electrode, the nonvolatile memory further comprising a gate electrode, a contact electrode, and a horizontal selection line, wherein the contact electrode is connected with the horizontal selection line, the source electrode and the drain electrode are arranged to extend in a direction crossing the horizontal selection line orthogonally, the gate electrode is arranged at a position above or below a region between the source electrode and the drain electrode, the position being apart 25 from the source electrode and the drain electrode, the conductive organic thin films are arranged so as to electrically connect the contact electrode, the source electrode, and the drain electrode, and the conductive organic thin film arranged between the contact electrode and the source electrode forms a memory part.
 13. The nonvolatile memory according to claim 12, wherein information is recorded utilizing a first conductivity for OFF and a second conductivity for ON, or contrarily, utilizing a first conductivity for ON and a second conductivity for OFF.
 14. The nonvolatile memory according to claim 12, wherein a transition from the first conductivity to the second conductivity is caused by applying a predetermined voltage to or flowing a predetermined current through the conductive organic thin films.
 15. The nonvolatile memory according to claim 12, wherein a ratio of a first conductivity in the second electric state to a second conductivity in the first electric state is 10² to 10¹⁰.
 16. The nonvolatile memory according to claim 12, wherein a transistor including the conductive organic thin films as an active layer, and the conductive organic thin film functioning as a memory are present on substantially the same plane.
 17. The nonvolatile memory according to claim 1, wherein the conductive organic thin film is either a monomolecular film or a build-up film obtained by laminating monomolecular films.
 18. The nonvolatile memory according to claim 1, wherein the conductive organic thin film has a conductivity (ρ) of not less than 1 S/cm at room temperature (25° C.) without a dopant.
 19. The nonvolatile memory according to claim 18, wherein the conductive organic thin film has a conductivity (ρ) of not less than 1×10³ S/cm at room temperature (25° C.) without a dopant.
 20. The nonvolatile memory according to claim 19, wherein the conductive organic thin film has a conductivity (ρ) of not less than 5×10⁵ S/cm at room temperature (25° C.) without a dopant.
 21. The nonvolatile memory according to claim 1, wherein the conductive organic thin film further contains a dopant substance. 